1. Field of the Invention
The present invention relates to a section of a rotatable drive line for transmitting torque between an input end and an output end. More particularly, the present invention relates to a power transmission line section in the form of an articulated drive shaft that can accept and transmit torque when the input and output ends of the line section are axially and angularly offset from each other.
2. Description of the Related Art
Power transmission sections in which the power input end of the transmission section is either intermittently or continuously axially or angularly offset from the power output end are utilized in numerous drive system applications. Examples of such applications include automotive drive trains and power transmission sections utilized in downhole drilling systems for drilling oil and gas wells.
In that regard, in downhole drilling systems utilized in drilling applications, progressive cavity pumps are provided and are operated in reverse, as motors, and are referred to as power sections of a drill string. The motors are commonly referred to as “mud motors” and are fluid-powered to provide output torque to drive a rotatable drill bit. Such motors have a rotor in the form of a helical stainless steel shaft that is rotatable within a stator. The stator is a formed, molded tubular elastomeric sleeve that is contained within a tubular metal casing. The inner surface of the stator is of helical form. The rotor is also of helical form and has a lobed cross section. The tubular stator has a lobed cross section with a dissimilar number of lobes as compared with the lobed cross section of the stator. Other forms of power sections can have a square outside cross section or a helical cross section. Power section types with improved torque output and horsepower are presently under development.
The mud motor of a downhole drilling system power section is located downhole, within a drill casing and near the drill bit. When drilling mud is pumped downhole under pressure to and through the mud motor, the result is that the downwardly moving drilling mud causes the rotor to rotate within the stator. The downstream end of the mud motor rotor thus rotates and simultaneously moves in an orbital path to provide orbital rotary motion to the input end of the power transmission section that is operatively connected at its output end to the drill bit. Thus, a universal-joint-type arrangement is needed to convert the orbital rotary input motion to pure rotation without orbital motion at the output end to drive the drill bit about a fixed axis of rotation.
Although a number of different articulating power transmission section arrangements have been disclosed and utilized in downhole drilling systems, many have been limited in their torque transmission capability and in their fatigue life. Additionally, the drilling mud that is utilized to drive the mud motor is of an abrasive nature, and unless they are adequately protected from the drilling mud the articulating ends of the power transmission section can quickly wear, requiring frequent drill string shutdowns for replacement of power transmission section components. There is presently a demand for downhole power sections capable of transmitting higher torque, and also capable of longer operating times before parts replacements are needed.
There is therefore a need for a power transmission section that is capable of transmitting a higher torque and that has a longer effective operating life than currently available power transmission section, and it is an object of the resent invention to provide such a power transmission section.